https://ftp.mozilla.org/pub/thunderbird/releases/ first pick the version you want, and then drill down to OS

Thanks for the reply. However the list is extensive and I don't know what version would work with my older OS. Where would be the dates that use my OS on those listed, so I don't have to guess. Any place that reverses the info: OS/Thunderbird version(s)?

Pat N

I did a web search and found this: https://thunderbird.macupdate.com/app/mac/11942/thunderbird/old-versions

TB 115.8.0 is the last version to support 10.13.5 (10.12 minimum). Choose the installer in your language from here:

https://archive.mozilla.org/pub/thunderbird/releases/115.18.0/mac/

So do I just copy all of the listed files(?) to get the complete program? Or is there a downlink somewhere? Thanks for the info, BTW

click to the folder for your language, (such as En-US, if English and United States) and there are two files.

I did a web search and found this: https://thunderbird.macupdate.com/app/mac/11942/thunderbird/old-versions

That list is outdated when Tb 115.18.0esr was the last Thunderbird version to still support the EOL macOS 10.12, 10.13, 10.14 and not the older Tb 115.12.2esr.

Thunderbird and Firefox from 116.0 to current versions requires macOS 10.15 (ten.fifteen) at minimum to run.

Firefox 115.31.0esr is the current version to support macOS 10.12, 10.13, 10.14 https://support.mozilla.org/en-US/kb/firefox-users-macos-1012-1013-1014-moving-to-extended-support

So do I just copy all of the listed files(?) to get the complete program? Or is there a downlink somewhere? Thanks for the info, BTW

In https://archive.mozilla.org/pub/thunderbird/releases/115.18.0/mac/ pick your language which is likely one of the English options as in en-CA, en-GB, en-US (Canadian, United Kingdom (Great Britain), US) then download the Thunderbird 115.18.0.dmg file.

This article gives you the basics on how to install the Thunderbird dmg file you downloaded. https://support.mozilla.org/en-US/kb/installing-thunderbird-on-mac